1. Field of the Invention
The present invention relates to a positioning device that determines position by receiving a signal from a positioning satellite, a positioning method, and a storage medium.
2. Description of the Related Art
Conventionally, there have been electronic devices having a global positioning system (GPS) function which intermittently determine position at predetermined time intervals, or those which determine position in conjunction with a certain operation such as shooting an image with a camera (refer to, for example, Japanese Patent Application Laid-Open (Kokai) Publication No. 2002-267734, Japanese Patent Application Laid-Open (Kokai) Publication No. 2006-339723, and U.S. Pat. No. 6,995,792).
GPS positioning devices calculate a pseudo range to each of a plurality of GPS satellites based on positional codes received from the GPS satellites, and after calculating the position of each GPS satellite based on ephemeris information, determine their own positions using these calculation results.
Once received, this ephemeris information can be used for several hours to calculate the position of a single GPS satellite. Therefore, in a typical GPS positioning device that intermittently determines its position, ephemeris information received during a previous positioning processing is stored in the memory, and if there is valid ephemeris information in the memory at the time of the subsequent positioning processing, the position of the device is quickly determined using this ephemeris information.
Radio waves transmitted from a GPS satellite are weak spread-spectrum radio waves, and in order to capture and demodulate these radio waves, the transmitting end and the receiving end are required to be synchronized when reception processing therefore is performed.
However, although the GPS satellite has accurate time information from an atomic clock, a clock circuit mounted in the receiving-end device is not as accurate. If there is any margin of error in the time clocked by the clock circuit, capturing and demodulating the radio waves consume more time due to mismatched timing between the transmitting end and the receiving end.
Accordingly, there is a problem in conventional positioning devices in that, even when valid ephemeris information has been stored therein and thus their position should be determined in a short amount of time, capturing radio waves consumes time due to the margin of error in the clocked time, and consequently the total amount of time required for the positioning is increased.